Amplitude-modulation-frequency-modulation antenna



Oct. 23, 1951 NELSON r 2,572,183

AMPLITUDE MODULATION-FREQUENCY MODULATION ANTENNA Filed April 28, 1949 INVENTORS fatenteci bet. 2 3;

AMPLITUDE -MODULATIONFREQUENCY- MODULATION ANTENNA Frank H. Nelson, Philadelphia, Pa., and Robert H. Dreisbach, Fort Wayne, Ind., assignors to The Magnavox Company, Fort Wayne, Ind., a corporation of Delaware Application April 28, 1949, Serial No. 90,156

9 Claims. (01. 250-20) It has long been common practice to provide commercially manufactured radio receiving sets capable of reception of signals in several widely spaced Wave bands, as, for example, the frequency modulation band of 88 to 108 megacycles, a short Wave band of 4 to 18 megacycles, as well as the standard broadcast band of 550 to 1600 kilocycles. These sets are ordinarily provided with a wave band switch whereby separate tuning circuits are used for reception of the different frequencies. The potential usefulness of the multiple band sets has heretofore been greatly limited by the antenna requirements, however, since it is well known that no conventional antenna willrespond satisfactorily to frequencies in these three widely spaced bands. It has therefore been necessary-to provide each receiver of this type with two or more antennas, each with a separate lead-in and a switching arrangement to selectively connect the tuning circuits of the receiver to any one of the antennas in order to get efiicient reception over all wave bands covered.

It is the general aim of the present invention to provide an antenna system having but one lead-in, so that no antenna switching is necessary, yet capable of high gain performance on each of several different wave bands of widely varying frequency. The accomplishment of this general aim involves several aspects. One advantage is the elimination of the switching heretofore required. Another is the simplification of the system by the use of one lead-in for all of the bands. The reduction of noise due to lead-in interference is a further consideration. Also, it is important to attain the desired performance by an antenna that is simple, inexpensive, and adapted to easy installation; even by persons havin little mechanical skill and no knowledge of electronics. Most important, however, is the necessity of providing an antenna system wherein wanted signal frequencies in any of the bands are transmitted to the receiver without serious losses, yet wherein unwanted signals are eifecitvely suppressed.

It is therefore a primary object of the present invention to accomplish these aims by the provision of an antenna system comprising a dipole section resonant in the range of the high est frequencies to be received (that is, the FM band) and a straight wire antenna suited to reception of the short wave and broadcast signals; with only one lead-in, which consists of a transmission line extending to a transformer at the receiver set. The accomplishment of this ebject also avoids the need of antenna switching arrangements. A further object of the invention is to accomplish these functional results by the provision of an antenna of simple and inexpensive physical structure, designed to be unobtrusive in appearance, strong and durable, yet so constructed that it may be easily installed in almost any desired location, even by persons untrained in electronics or the mechanical arts.

According to these teachings these objects are accomplished by a system which includes means to isolate the dipole from the straight section during FM reception, so that signal energy received on the dipole will not be dissipated but will be fed to the receiver without substantial losses. Also, means are provided to suppress high frequency signals that may be imposed on the straight section of the system so that interference will not result, yet to transmit lower frequency signals from this section to the lead-in without substantial losses. These functions are accomplished in the present teaching by the provision of a novel antenna transformer having two primary sections tuned to the broadcast and short wave bands respectively, together with a secondary connected to the lead-in through an isolation transformer consisting of a length of transmission line so related to the impedance of the antenna transformer secondary as to present an extremely high impedance value at the point of connection between the dipole and lead-in. It follows that substantially all of the signal energy received on the dipole Will be fed through the lead-in to the set.

A present preferred embodiment of the invention is illustrated in the drawings of this disclosure wherein:

Figure 1 is a diagrammatic view of an antenna system as here contemplated;

Figure 2 is a schematic diagram of the antenna transformer utilized in the system of Figure 1; and v Figure 3 is a schematic diagram of the receiver transformer as here contemplated.

As shown, the structure consists of a relatively lon span of wire extending between the insulators H and I2 which may be secured to any supporting surfaces represented by the masts I3 and M. The span of wire between these two insulators is not continuous in an electrical sense but consists of a relatively long straight wire section [5 extending from the insulator l2 to an intermediate insulator l6 and a dipole section comprising elements ll and is separated by a spacing insulator I9. The innerends of the dipole elements 11 and 18 are directly connected to the paired conductors 2i and 22 of the lead-in generally designated as 23 which extends to a receiver transformer 24. The straight section of the system, which functions to receive broadcast and short wave signals, is inductively coupled to'the lead-in 23 through an'ante'nna transformer 25 and an insolation transformer 26 which may consist of a predetermined length of, dual conductor transmission line joined to the inner ends of the dipole elements If and i8 at their point of connection with the lead-in conductors 2| and 22.

The antenna transformer 25 may be physically mounted within the insulator l6. Its c'ircuifiis preferably arranged according to the schematic circuit diagram of Figure 2. The straight wire section I5 of the system feeds directly to atra ns former primary winding consisting of two differently tuned sections 3! and 32,. bridged'by the condensers 33 and 34 respectively. The circuit 3|-33 is tuned to the shortwave band and the section 32-454 is tunedto the broadcast band. The circuit from the straight wire section of the antenna system extends through these sections in series and thence to ground by way of the conductor 35. w

The secondary winding of the antenna transformer consists of two separate sections 35 and 31, corresponding to the sections 31 and 32 of the primary winding and similarly tuned. The winding 37 is bridged by capacitor 38, and the sections 35 and 3! are connected in series with each other. They are also connected through the length of transmission line 26 to the lead-in at the point of connection between the lead-in and the inner ends of the dipole sections.

The receiver transformer, generally designated at 24 has windings as schematically shown in Figure 3. The primary winding comprises three sections 4|, 42 and 43 in series. The sections t2 and A3 are bridged by capacitors 44 and 45 respectively. The values of inductance and capacitance are such that the sections 4!, 42 and 43 are tuned to the FM band, short wave band, and broadcast band respectively. This transformer includes two secondary windings. The winding 36 is tuned to the FM band and has leads extending directly to output terminals 41 and 43. The other secondary winding comprises a section 5| tuned to the short wave band, in

series with a section 52 bridged by the capacitor 53 and tuned within the frequency range of the broadcast hand. These windings are connected to the output terminals 54 and 55 which leadto the tuning circuits of the AM and short wave receiver. If desired, one of these output terminals may be grounded so that the lead-in circuit, which is balanced from the antenna transformer 25 to the receiver transformer 24, is converted to an unbalanced line for feeding the receiver.

Operation The operation of the system is as follows: When signals of standard broadcast frequencies are being received the signals will be impressed on the long straight wire section [Sand will thence be fed through the sections SI and 32 of the antenna transformer primary and to ground. The field set up by passage of the signal current through the winding 32 of the transformer primary will induce a corresponding signal in the secondary 31. The signal is fed through the isolation section 26 of the transmission line to the lead-in 23 and thence to the receiver transformer 24. At short wave and broadcast frequencies the dipole elements I! and [8 have negligible effect on the characteristics of the transmission line, so that the lead-in 23 and isolation portion 26 function only as a continuous balanced line through which the signal is transmitted from the antenna transformer 25 to the receiver transformer 24. At the receiver transformer the signal is fed through the primary and induced into the secondary through the sections #3 and 52 which are." tuned to the broadcast frequency. The signalthus appears at the output terminals 54 and55 leading to the receiver.

When receiving signals in the short wave band, mesysa irunants in the same manner as described above with the exception that the coupling in 'thean'tenna transformer 25 is accomplished primarily between the windings 3| and S'Sfwhich are tuned to the short wave band. Similarly, in the receiving transformer 24 the coupling is acco plished primarily in the central sections 42 and 5| of the primary and secondary windings.

In receiving a frequency modulation signal (that is, a signal in the 88 to 108 megacycle band), any signal appearing on the straight section 15 of the, antenna will be suppressed, since the primary windings 3| and 32 of the antenna transformer will function as aneffective radio irequencyjchoke. This is effective to minimize any ossibility of mutual coupling between the straight section |5fof.the antenna and dipole elements as Well as to reduce the energy transfer in the transformer toa negligiblevalue.

The dipole elements I] and I8 will respond to the FM'signal, however, so that the signal energy appears as a current source across the insulator I9. By viewing Figure 1 ofthe drawing it will be seen. that there are two. possible paths for current flowing from this source. One path is through .the lead-in 23 and. primary of the receiver transformer 24. The other path is through the section 2B of the transmission line and'thr'ough the secondary windings of the antenna transformer 25. By the teachings of this invention the'finputfi'mpedance values of these two paths are so'relatedlf't'hat the path to the antenna transformer presents an extremely high impedance; far above the input impedance presented by the lead-in- Thus substantially all of the signal energy is fed down thelead-in to the receiver transformer andthence to the set.

It is a known phenomenon that a quarter-wave section of lossless transmission line, when shortc ircuited, presents an infinite impedance to a signal imposed upon. it, and that odd multiples of such 'a quarter-wavesection exhibit similar characteristics. When the line is not short-circuited, but is terminated by an impedance ZR the input impedance Zs in a lossless line maybe designated. by the following formula when the characteristic impedance iS Rc iQS lengths, and phase constant I lized by'designing the antenna transformer 25'.

so'thatthe length of the isolation sections of the transmission 'lineandthe impedance Za of the transformer winding combine to present an extremely high input impedance to this current,

path when viewed from the separating, insulator [9 at the junction of theldipole sections and the lead-in. Thus this branch of the circuit may be said to have an electrical length substantially equal to an odd quarter wave section of transmission line, and to present an extremely high impedance to any signal appearing on the dipole.

It is a known theorem that a current imposed on parallel impedances will divide itself in a manner inversely proportional to absolute magnitude of each of them. Thus the possible path of current flow through the isolation section 26 will present an impedance greatly exceeding the impedance presented by the lead-in to the receiver transformer. It follows that substantially all of the signal energy will flow through the lead-in to the receiver transformer and will be induced from the primary section 4| into the secondary winding 46 so that the signal will appear at the output terminals 41 and 48.

From the foregoing it is believed apparent that the teachings of this invention accomplish the intended aims and objects, since an antenna according to the present disclosure is capable of high gain performance in the standard broadcast band, short wave band and in the'frequency modulation band, yet these signals are received without interference between the different sections of the antenna and are fed to the receiver through a common lead-in so that no antenna switching is required. The system inherently suppresses noise due to stray voltages induced in the lead-in section, since any noise voltages induced therein will be equal in magnitude and in phase in the two conductors of the line. Thus these voltages will appear in the transformer windings in phase opposition, and will result in zero noise current.

An antenna according to these teachings is extremely simple in its physical structure and may be manufactured easily and economically. Moreover, it may be conveniently installed in almost any location, since it is only necessary to suspend the opposite insulators H and I2 between any supports conveniently available. Obviously the installation requires no technical knowledge, but may be made by anyone, even though not skilled in the mechanical or electrical arts. In short, the teachings of the present invention offer a Simple, feasible and economically practical solution for a problem that has defied other attempts at solution throughout a period of years, despite a long felt and universally recognized need.

Having thus described the invention, what we claim as new and desire to protect by United States Letters Patent is:

1. An antenna system comprising, in combination, a single wire adapted to be suspended between a pair of insulators, with additional insulators dividing it into two aligned sections comprising a dipole section and an unbalanced straight wire section of length greatly exceeding the length of the dipole section and responsive to lower frequencies than the dipole section; a lead-in consisting of a dual lead transmission line coupled to said dipole section; an antenna transformer having a primary winding comprising two difierently tuned sections in the circuit of the straight wire section and a secondary winding comprising two differently tuned sections; and an isolation transformer consisting of a section of dual lead transmission line coupled between said secondary winding of the antenna transformer and the dipole elements; with the input impedance of said section of transmission line and secondary of the antenna transformer straight wire section of length greatly exceeding the length of the dipole section and responsive to lower frequencies than the dipole section; a

lead-in consisting of a dual lead transmission line coupled to said dipole section; an antenna transformer having a primary winding comprising two differently tuned sections in the circuit of the straight wire section and a secondary winding comprising two differently tuned sections; and an isolation transformer consisting of a section of dual lead transmission line coupled between said secondary winding of the antenna transformer and the dipole elements; with the total electrical length of the said section of transmission line and antenna transformer secondary substantially equal to an odd multiple of a quarter wave length of the resonant frequency of the dipole section.

3. An antenna system comprising, in combination, a single wire adapted to be suspended between a pair of insulators, with additional insulators dividing it into two aligned sections comprising a dipole section and an unbalanced straight wire section of length greatly exceeding the length of the dipole section and responsive to lower frequencies than the dipole section; a lead-in consisting of a dual lead transmission line coupled to said dipole section; an antenna transformer having a primary winding in the circuit of the straight wire section and a secondary winding; and an isolation transformer consisting of a section of dual lead transmission line coupled between said secondary winding of the antenna transformer and the dipole elements; with the input impedance of said section of transmission line and secondary of the antenna transformer greatly exceeding the input impedance of the lead-in.

4. An antenna system comprising, in combination, a single wire adapted to be suspended between a pair of insulators, with additional insulators dividing it into twoaligned sections comprising a dipole section and an unbalanced straight wire section of length greatly exceeding the length of the dipole section and responsive to lower frequencies than the dipole section; a lead-in consisting of a dual lead transmission line coupled to said dipole section; an antenna transformer having a primary winding in the circuit of the straight wire section and a secondary winding; and an isolation transformer consisting of a section of dual lead transmission line coupled between said secondary winding of the antenna transformer and the dipole elements; With the total electrical length of the said section of transmission line and antenna transformer secondary substantially equal to an odd multiple of a quarter wave length of the resonant frequency of the dipole section.

5. An antenna system comprising, in combination, a dipole section; an unbalanced straight wire section of length greatly exceeding the length of the dipole section and responsive to lower frequencies than the dipole section; a leadin consisting of a dual lead transmission line coupled to said dipole section; an antenna transformer having a primary winding in the circuit of the straight wire section and a secondary winding; and an isolation transformer consisting of a section of dual lead transmission line coupled between said secondary winding ofthe antenna transformer and the dipole elements; with the input impedance of said section of transmission line and secondary of the antenna transformer greatly exceeding the input impedance of the lead-in, the total electrical length of the said section of transmission line and antenna transformer secondary being substantially equal to an odd multiple of a quarter wave length of the resonant frequency of the dipole section.-

6. An antenna system comprising, in combination, a single wire adapted to lee-suspended betweena pair or insulators, with additional insulators dividing it into two aligned sections comprising a dipole section balanced to ground and resonant to a frequency within the 88 to I08 megacycleFM band and anunbalanced straight wire section of length greatly exceeding. the length of the dipole section and responsive to lower frequencies than said dipole sections; a lead-in consisting of a dual lead transmission line coupled to said dipole section; an antenna transformer having a primary winding comprising two differently tunedsections in the circuit of the straight wire section and a secondary winding comprising two differently tuned sections; and an isolation transformer consisting of a section of dual lead transmission line coupled between said secondary winding of the antenna transformer and the dipole elements; and a receiver transformer having a primary winding coupled to said lead-in and consisting of three difierently tuned sections and two secondary windings, one of which consists of two differently tuned sections.

7. An antenna system comprising, in combination, a single wireadapted to be suspended between a pair of insulators, with additional insulators dividing it into two aligned sections comprising a dipole section balanced to groundand an unbalanced straight wire section of length greatly exceeding the length of the dipole section and responsive to lower frequencies than said dipole section; a lead-in consisting of a dual lead transmission line coupled to said dipole section; an antenna transformer having a primary winding comprising two differently tuned sections in the circuit of the straight Wire section and a secondary winding comprising two difierently tuned sections; and an isolation transformer 0011-.

sisting of a section of dual lead transmission line coupled between said secondary winding of the antenna transformer and the dipole elements; and a receiver transformer having a primary winding coupled to said lead-in and consisting of three difierently tuned sections and two sec- 8 ondary windings; one of which consists of two differently tuned sections.

8. An antenna-system comprising, in combina-- tion, a single wire adapted to be suspended be tween apair ofinsulator-s,- with additional insu latorsdividing it into two aligned sections comprising a dipole section balanced to ground and an unbalanced straight wire section of length greatly exceeding the length of the dipole section and responsive to lower frequencies than said dipole section; a lead-inconsisting of a dual lead transmission line coupledto said dipole section; an antenna transformer having a primary winding in the circuit of the straight wiresection and aseconda'ry winding and an: isolation trans former consisting of a section of dual lead transmission line coupled between said secondary winding of the antenna transformer and the dipole elements; and a receiver transformer coupled to said lead-in and having a primary winding and secondary winding.

9. An antennasystem comprising, in combination, a dipole section; an unbalanced straight wire section of length greatly exceeding the length of the dipole section and responsive to lower frequencies than the dipole section; a lead-in consisting of a dualv lead transmission line directly connected to the dipole section; .a receiver transformer having a primary winding connected directly across the leads of the transmissionline; an antenna transformer having a primary wind ing in the circuit of the straight wire section and a secondary winding and an isolation transformer consisting of a section of dual lead transmission line coupling the secondary winding of the antenna transformer to the point of connection between the-dipole elements and the lead-in; with the input impedance of said section of transmission line and secondary of the antenna transformer greatly exceeding the input impedance of the lead-in and'receiver transformer.

FRANK NELSON. ROBERT H. DREISBACH.

REFERENCES CITED The following references are of record inthe file" of this patent:-

UNITED STATES PATENTS Number Name Date Re. 19,854 Amy et al. Feb. 18, 1936 2,021,734 Macalpine Nov. 19, 1935 2,074,896 Earnshaw Mar. 23, 1 937 Dome May 10, 2,143,159 Lundahi Jan. 10, 1939 2,189,309 Carlson Feb. 6, 1940 2,222,406 Crossley Nov. 19, 1940 

